Sustainable separation of petroleum hydrocarbons pollutant using hydrophobic deep eutectic solvents regulated by CO2

Abstract Petroleum hydrocarbons pollutants are the serious environmental hazards in the exploitation of petroleum resources. As comparison to the traditional solvent for petroleum hydrocarbons removal, deep eutectic solvents (DESs), as the ideal alternate for organic solvents, have non-toxicity, non-flammability and lower volatility. Whereas, the recycling of DES is still the great challenge for sustainable separation. Herein, hydrophobic DESs (HDESs) with the CO2 switchable-hydrophilicity are developed, aiming to sustainably separate petroleum hydrocarbons pollutions. The HDESs are formed by hydrogen bonds between the phenolic compounds as hydrogen bond donors (HBDs) and tertiary amines as hydrogen bond acceptors (HBAs), which was demonstrated by the spectroscopic detection. Interestingly, the HDES exhibits better CO2-switchable behavior than traditional switchable-solvent, where the phase transition is induced by the protonation of HBA upon CO2 and the deprotonation of HBD in HCO3- solution of HBA. Furthermore, the sustainable separation for oils (heptane, diesel oil and crude oil) is successfully completed, and the HDES is also easily recovered upon N2/65 °C. Finally, the HDES is effectively applied in removing petroleum hydrocarbons from oily wastes (oil sands and oily sludge). The results show that more than 98% oil is removed from oil sands, and 85.02% oil is also removed from oily sludge. Thus, the HDESs will be expected to treated as the effective extractant for sustainable and cleaner separation of petroleum hydrocarbons- contaminated waste.